The present invention relates to a shutoff and control slide of the type including a cylinder having therein radial openings, the cylinder having a sliding sleeve axially displaceable therein, in particular a sliding sleeve having openings therein, and packing means extending between the cylinder and the sliding sleeve for the purpose of sealing the opening of the cylinder when it is covered by the sliding sleeve.
Shutoff and control slides of the type described above have been disclosed repeatedly and are known to include an embodiment having slot-shaped openings in the cylinder and possibly also in the sliding sleeve, especially in association with hot blast furnaces, particularly of the Cowper type. In any case, a space surrounding the openings is adjacent to the exterior of the cylinder, which space must be shut off completely or in a controlled manner, by means of the shutoff and control slide, in relation to a second space that communicates continuously with the interior of the sliding sleeve. These two spaces are referred to in the following text as housing connections. The sliding sleeve is displaced axially in the cylinder by means of any suitable drive, both for complete shutting off and also for variable control. Thus, the opening of the cylinder is thus covered completely or in part by the sliding sleeve. In order to achieve satisfactory displacement of the sliding sleeve in the cylinder, while also insuring satisfactory reciprocal sealing between the above mentioned housing connections, piston rings have been employed. However, tests have shown that, in the case of a shutoff and control slide of the above mentioned kind used in connection with a hot blast furnace, the piston rings between the sliding sleeve and the cylinder of such a slide can only produce a seal that is not capable of meeting all requirements of load and operation for relatively long periods of time, due to the relatively slow progress of displacement operations and due to the long periods of rest of the sliding sleeve in its outer or end limit positions. Also, the costs for machining the cylinder are relatively high, and, finally, costs are also high due to the susceptibility of the piston rings to corrosion.